Jul 23 10:00 PM PDT  11:00 PM PDT This period of time is long enough: it gives you more than enough time to comfortably learn, review and practice all of the material. On the other hand it is not too long. Jul 24 11:30 PM EDT  10:00 PM EDT Free GRE Class: First Session. Experience the power of live instruction, for free. Our sample classes showcase our passionate and dedicated faculty and the way they'll guide you through proven strategies for improving your score. Jul 25 07:00 PM EDT  08:00 PM EDT Strategies and techniques for approaching featured GRE topics. An introduction to one of Manhattan Prep’s GRE worldclass instructors. Jul 29 10:00 PM PDT  11:00 PM PDT A Revolutionary OnDemand GRE Prep Course. Try for $1 Jul 30 10:00 PM PDT  11:00 PM PDT 7+ POINT GRE SCORE IMPROVEMENT GUARANTEE Jul 31 10:00 PM PDT  11:00 PM PDT Sign up for 1 Week GRE Prep
Author 
Message 
TAGS:


Founder
Joined: 18 Apr 2015
Posts: 7401
Followers: 125
Kudos [?]:
1449
[0], given: 6611

The 500 students in a class took an examination. Sco [#permalink]
22 Aug 2017, 02:16
Question Stats:
26% (01:32) correct
73% (01:53) wrong based on 38 sessions
The 500 students in a class took an examination. Scores were given on an integer scale of 0100. Jamal's score was 2 standard deviations above the mean score on the examination, and Charlie's score was at exactly the 5th percentile. The distribution of exam scores was approximately normal. Which of the following statements must be true? Indicate all such statements. ❑ Jamal scored closer to the mean than Charlie. ❑ More than 400 students achieved scores less than or equal to Jamal's score and greater than or equal to Charlie's score. ❑ Fewer than 450 students achieved scores less than or equal to Jamal's score and greater than or equal to Charlie's score. ❑ At least one other person received the same score as Charlie.
_________________
Get the 2 FREE GREPrepclub Tests




Manager
Joined: 15 Jan 2018
Posts: 147
GMAT 1: Q V
Followers: 3
Kudos [?]:
188
[2]
, given: 0

Re: The 500 students in a class took an examination. Sco [#permalink]
23 Apr 2018, 19:00
2
This post received KUDOS
A: You need to know that in a normal curve, the mean is exactly at the 50%ile, 1 standard deviation above the mean is 34%ile above that, and 2 standard deviations above the mean is 14%ile above that. In other words, 2 standard deviations above the mean is around 98%ile. Since Jamal is therefore at 98%ile and Charlie as at 5%ile, Charlie is closer to the mean and this answer is out. B: If Charlie is 5%ile, then he performed better than 5% of the total, or 25 people. Since Jamal is 98%ile, he performed better than 98% of the students, meaning about 2% of them, about 10 students, performed better than him. Since only about 35 people out of 500 performed either better or worse than them, 465 must have performed equal to Charlie or above or equal to Jamal or below, so we can see that this answer must be true. C: From the last answer choice, we know that we're looking at 465 people, which is well above 450, so this one is out. D: Since there are 500 students, every percentile must contain 5 students. The key to this one is the word "exactly". Since the 5th percentile falls between the 25th and 26th student, the 5th percentile itself is the average of the 25th and 26th students' scores. Since the scores are given in integers, if you average two of them, you'll either get an integer, or something that ends in a .5. But since Charlie couldn't have gotten a score that ends in a .5, this scenario is out. What if the 25th lowest student had scored a 20 and the 26th lowest had gotten a 22? Then the 5th percentile would be 21, but since nobody actually got that score, this scenario is impossible. The only way Charlie could've gotten exactly the 5th percentile is if the 25th and 26th lowest people got the same score, in which case the average of the two of them equals both of them. Thus, D is in.
_________________
    
Need help with GRE math? Check out our groundbreaking books and app.



Founder
Joined: 18 Apr 2015
Posts: 7401
Followers: 125
Kudos [?]:
1449
[0], given: 6611

Re: The 500 students in a class took an examination. Sco [#permalink]
24 Apr 2018, 01:45
Amazin explanation. As usual. I missed it.
_________________
Get the 2 FREE GREPrepclub Tests



Intern
Joined: 14 Jun 2018
Posts: 36
Followers: 0
Kudos [?]:
7
[0], given: 100

Re: The 500 students in a class took an examination. Sco [#permalink]
28 Jul 2018, 01:48
Carcass wrote: Amazin explanation. As usual.
I missed it. Hello Carcass. Charlie score is at 5th percentile, which means p5. To find p5, we have to follow those steps: 1: position of p5 is L = 5 * (501)/100 = 25.05 2: M = 25 3: P5 = X25 + (25.0525)(2625) = 25.05 I don't understand exactly how D is resolved! I just did the previous logic while i was trying to approach for a solution.



GRE Prep Club Legend
Joined: 07 Jun 2014
Posts: 4809
WE: Business Development (Energy and Utilities)
Followers: 123
Kudos [?]:
1972
[1]
, given: 397

Re: The 500 students in a class took an examination. Sco [#permalink]
29 Jul 2018, 13:24
1
This post received KUDOS
Avraheem wrote: Hello Carcass. Charlie score is at 5th percentile, which means p5. To find p5, we have to follow those steps:
1: position of p5 is L = 5 * (501)/100 = 25.05 2: M = 25 3: P5 = X25 + (25.0525)(2625) = 25.05
I don't understand exactly how D is resolved! I just did the previous logic while i was trying to approach for a solution.
Hi, Could you please clarify what you mena by X25 and M. Percentile score is that score which divides the highest value in the previous bracket and the lowest value in the next %tile bracket. For example 1% means the score of the 5th and 6th student averaged. So suppose we have the following score card Student Rank: 1...2...3...4...5...6...7...8...9...10...11...12 Score: 12..14..14..15..15..16..17..17..17..18..18..19 1%ile score in the case above is 15.5. No one gets exactly one percentile. However 2%tile score is 18. Student number 10 and 11 both have that score. In order to get an integer percentile you must have the last member of previous bracket and the first member of current bracket with thw same score. Hence atleast one other guy must have scored the same points as charlie has an integer value of percentile.
_________________
Sandy If you found this post useful, please let me know by pressing the Kudos Button
Try our free Online GRE Test



Intern
Joined: 27 Jan 2019
Posts: 25
Followers: 0
Kudos [?]:
19
[0], given: 3

Re: The 500 students in a class took an examination. Sco [#permalink]
23 Apr 2019, 20:14
Hello Sandy
I am rusty on this topic so i need some help in understanding these percentile questions. Why is 1 percentile 15.5 in the case u mentioned ? Shouldn't it be 1/100*12 or 13. I am not sure why do 1 is added to the total number of items when percentile position is calculated? Is it to exclude the percentile position we are calculating i.e to calculate the percentage of values below say 1 percentile , but not including the value of 1 percentile? please explain.



Intern
Joined: 02 Mar 2019
Posts: 45
Followers: 0
Kudos [?]:
4
[0], given: 48

Re: The 500 students in a class took an examination. Sco [#permalink]
13 Jun 2019, 11:21
A: You need to know that in a normal curve, the mean is exactly at the 50%ile, 1 standard deviation above the mean is 34%ile above that, and 2 standard deviations above the mean is 14%ile above that. In other words, 2 standard deviations above the mean is around 98%ile. Since Jamal is therefore at 98%ile and Charlie as at 5%ile, Charlie is closer to the mean and this answer is out.
Could someone explain this? Appreciate it!



Manager
Joined: 08 Dec 2018
Posts: 90
Followers: 0
Kudos [?]:
32
[0], given: 30

Re: The 500 students in a class took an examination. Sco [#permalink]
17 Jun 2019, 08:15
SherpaPrep wrote: A: You need to know that in a normal curve, the mean is exactly at the 50%ile, 1 standard deviation above the mean is 34%ile above that, and 2 standard deviations above the mean is 14%ile above that. In other words, 2 standard deviations above the mean is around 98%ile. Since Jamal is therefore at 98%ile and Charlie as at 5%ile, Charlie is closer to the mean and this answer is out.
B: If Charlie is 5%ile, then he performed better than 5% of the total, or 25 people. Since Jamal is 98%ile, he performed better than 98% of the students, meaning about 2% of them, about 10 students, performed better than him. Since only about 35 people out of 500 performed either better or worse than them, 465 must have performed equal to Charlie or above or equal to Jamal or below, so we can see that this answer must be true.
C: From the last answer choice, we know that we're looking at 465 people, which is well above 450, so this one is out.
D: Since there are 500 students, every percentile must contain 5 students. The key to this one is the word "exactly". Since the 5th percentile falls between the 25th and 26th student, the 5th percentile itself is the average of the 25th and 26th students' scores. Since the scores are given in integers, if you average two of them, you'll either get an integer, or something that ends in a .5. But since Charlie couldn't have gotten a score that ends in a .5, this scenario is out.
What if the 25th lowest student had scored a 20 and the 26th lowest had gotten a 22? Then the 5th percentile would be 21, but since nobody actually got that score, this scenario is impossible.
The only way Charlie could've gotten exactly the 5th percentile is if the 25th and 26th lowest people got the same score, in which case the average of the two of them equals both of them. Thus, D is in. Can you please explain why the 5th percentile score cannot be 21? thanks in advance.



Founder
Joined: 18 Apr 2015
Posts: 7401
Followers: 125
Kudos [?]:
1449
[0], given: 6611

Re: The 500 students in a class took an examination. Sco [#permalink]
17 Jun 2019, 08:57
If Jamal's score places him at approximately the 98_th percentile and Charlie's score was at the 5 percentile, then about 93% of the class scored between Jamal and Charlie since 93% of 500 is equal to 465. I hope now is more clear to you why B is correct. Regards
_________________
Get the 2 FREE GREPrepclub Tests



Intern
Joined: 27 Jan 2019
Posts: 25
Followers: 0
Kudos [?]:
19
[0], given: 3

Re: The 500 students in a class took an examination. Sco [#permalink]
06 Jul 2019, 10:01
Hi Carcass
Can you please share some theory on percentiles? I alway find these questions confusing. Hopefully some theory will help. Thanks



Founder
Joined: 18 Apr 2015
Posts: 7401
Followers: 125
Kudos [?]:
1449
[0], given: 6611

Re: The 500 students in a class took an examination. Sco [#permalink]
06 Jul 2019, 11:18
Sue Use the gmatclub math book at page 16. Percentile is rather a simple concept. The questions as worded become tricky. Attachment: feel free to ask further assistance regards
_________________
Get the 2 FREE GREPrepclub Tests



Intern
Joined: 27 Jan 2019
Posts: 25
Followers: 0
Kudos [?]:
19
[0], given: 3

Re: The 500 students in a class took an examination. Sco [#permalink]
08 Jul 2019, 05:23
Hi Carcass
If Charlie out scored 25 students then his score must be the 26th score or the first in the 6th percentile. Why is 5th percentile the average of 25th and 26th score? Why it is not the 26th score below which 5% of the scores or 25 values lie? Some user above has calculated the position of the 5th percentile as 5/100 *501 =25.05. Why is 1 added to the total?



GRE Instructor
Joined: 10 Apr 2015
Posts: 2175
Followers: 64
Kudos [?]:
1986
[2]
, given: 20

Re: The 500 students in a class took an examination. Sco [#permalink]
08 Jul 2019, 09:17
2
This post received KUDOS
fifan wrote: Hi Carcass
If Charlie out scored 25 students then his score must be the 26th score or the first in the 6th percentile. Why is 5th percentile the average of 25th and 26th score? Why it is not the 26th score below which 5% of the scores or 25 values lie? Some user above has calculated the position of the 5th percentile as 5/100 *501 =25.05. Why is 1 added to the total? I'm not crazy about question D. From what I've read in ETS's GRE literature, it's unclear how the GRE treats the calculation of percentiles when it comes down to the finer points. For example, in the set of ages {1, 2, 3, 4, 5}, some will say that the age of 3 is a 40th percentile age (since 3 is greater than 40% of the ages), while others will insist that 2.5 (the average of 2 and 3) is a 40th percentile age. So, for example, let's say the first 27 scores (out of 500 scores) are: 1,1,1,1,1,1,1,1,2,2,3,3,4,4,5,5,6,6,6,6,7,7,7,7,8, 9,10 The 26th score is 9So,there are 25 scores less than 925/500 = 5%, so some would say that 9 is a 5th percentile score. Others will say that 8.5 is the 5th percentile score. I don't believe I've seen an official GRE question that hinges on the one concept.
_________________
Brent Hanneson – Creator of greenlighttestprep.com Sign up for my free GRE Question of the Day emails



Intern
Joined: 27 Jan 2019
Posts: 25
Followers: 0
Kudos [?]:
19
[0], given: 3

Re: The 500 students in a class took an examination. Sco [#permalink]
08 Jul 2019, 23:01
Thanks Greenlight Prep What is most that GRE can ask about percentiles?From your post i assume the GRE wont ask to calculate a particular percentile value from a set of given values since as u mentioned there is a difference of opinion.



GRE Instructor
Joined: 10 Apr 2015
Posts: 2175
Followers: 64
Kudos [?]:
1986
[1]
, given: 20

Re: The 500 students in a class took an examination. Sco [#permalink]
09 Jul 2019, 05:43
1
This post received KUDOS
fifan wrote: Thanks Greenlight Prep What is most that GRE can ask about percentiles?From your post i assume the GRE wont ask to calculate a particular percentile value from a set of given values since as u mentioned there is a difference of opinion. I think the first 3 questions in this post are reasonable. If there were a question that hinged on the exact calculation of percentiles, the testmakers would include some additional proviso (e.g., here's how to calculate 33rd percentile) to help you answer the question. Cheers, Brent
_________________
Brent Hanneson – Creator of greenlighttestprep.com Sign up for my free GRE Question of the Day emails




Re: The 500 students in a class took an examination. Sco
[#permalink]
09 Jul 2019, 05:43





